Contacts in magnetic contactor are the part which suffer stress, heat due to mechanical movement, electrodynamic effect and arcs. Thus maintenance of contacts is a very important job and need to be done by skilled hand.
How to select a damaged or worn out contact in magnetic contactor
It is the hard part to choose which contact is good or bad. If the surface of the contact is rough & discolored, that does not mean that it is damaged and need to be replaced. In fact changing a contact in magnetic contactor for less important reason is prohibited as the contact in used is already ”electrically seated” and make good contact over a larger surface.
If any contact is to be replaced, all the three contact must be replaced by a same set of contacts plus the arc chutes also must be changed.
Maintenance of contacts in magnetic contactor